The present invention relates in general to methods and devices for regulating body temperature in humans and in particular to methods and devices for regulating body temperature in humans using skin temperature feedback.
Some closely related literature includes, in ascending chronological order: (1) Shitzer, A., Chato, J. C., and Hertig, B. A. Thermal protective garment using independent regional control of coolant temperature. Aerospace Med. 1: 49-59, 1973. (2) Veicsteinas, A, Ferretti, G, and Rennie, D W. Superficial shell insulation in resting and exercising men in cold water. J. Appl. Physiol. 52: 1557-1564, 1982. (3) Sawka, M N, Gonzalez, R R, Drolet, L L, and Pandolf, K B. Heat exchange during upper and lower body exercise. J. Appl. Physiol. 57: 1050-1054, 1984. (4) Johnson, J M, Brenglemann, G L, Hales, J R S, Vanhoutte, P M, and Wenger, C B. Regulation of the cutaneous circulation. Federation Proc. 45: 2841-2850, 1986. (5) Speckman, K L, Allan, A E, Sawka, M N, Young, A J, Muza, S R, and Pandolf, K B. Perspectives in microclimate cooling involving protective clothing in hot environments. International Journal of Industrial Ergonomics. 3: 121-147, 1988. (6) Pergola, P E, Kellogg, D L, Johnson, J M, and Kosiba, W. Reflex control of active cutaneous vasodilation by skin temperature in humans. Am. J. Physiol. 266 (Heart Circ. Physiol. 35): H1979-H1984, 1994. (7) Constable, S. H., Bishop, P. A., Nunneley, S. A., and Chen, T. Intermittent microclimate cooling during rest increases work capacity and reduces heat stress. Ergonomics. 37(2): 277-285, 1994. (8) Bomalaski, S. H., Chen, Y. T., and Constable, S. H. Continuous and intermittent personal microclimate cooling strategies. Aviat. Space Environ. Med. 66(8): 745-750, 1995. (9) Pergola, P E, Johnson, J M, Kellogg, D L, and Kosiba, W. Control of skin blood flow by whole body and local skin cooling in exercising humans. Am. J. Physiol. 270 (Heart Circ. Physiol. 35): H208-H215, 1996. (10) Xu, X., Hexamer, M., and Wemer, J. Multi-loop control of liquid cooling garment systems. Ergonomics. 42(2): 282-298, 1999. (11) Nyberg, K. L., Diller, K. R., and Wissler, E. H. Model of human/liquid cooling garment interaction for space suit automatic thermal control. J. Biomechanical Engineering. 123: 114-120, 2001. (12) Cheuvront, S. N., Kolka, M. A., Cadarette, B. S., Montain, S. J., and Sawka, M. N. Efficacy of intermittent, regional microclimate cooling. J. Appl. Physiol. 94: 1841-1848, 2003. (13) Thomley, L. J., Cheung, S. S., and Sleivert, G. G. Responsiveness of thermal sensors to nonuniform thermal environments and exercise. Aviat. Space Environ. Med. 74: 1135-1141, 2003. (14) Xu, X., Berglund, L. G., Cheuvront, S. N., Endrusick, T. L., and Kolka, M. A. Model of human thermoregulation for intermittent regional cooling. Aviat. Space Environ. Med. 75: 1065-1069, 2004.
Many occupations (e.g., firefighters, soldiers, astronauts, explosive ordnance, toxic waste clean-up) require workers to wear personal protective equipment (PPE) with characteristic high insulation (clo) and low moisture permeability (im) properties. These conditions impose uncompensable heat stress (required evaporative cooling exceeds evaporative cooling capacity of environment) that results in rapid heat storage and a reduction in work capabilities. Specifically, physical and cognitive performance is severely compromised and heat strain becomes overwhelming in a relatively short period.
Present-day microclimate cooling (MCC) systems are designed to remove heat from the skin using ice-packet vests, cooled air, or by circulating cooled liquid in tubes. Each of these methods is effective in reducing heat strain and extending work performance. For most military, space, and firefighting applications, liquid-cooled systems have several advantages over other MCC approaches, including reduced logistical requirements and sustainable high cooling capacities.
Engineering approaches for developing liquid MCC systems have focused on enhancing MCC efficacy by reducing coolant temperatures or increasing coolant flow. However, these engineering approaches increase MCC power (battery) requirements. Ironically they may also reduce heat transfer potential in certain situations. Skin cooling produces cutaneous vascular constriction that decreases convective heat transfer from the body core to the periphery. Superficial shell insulation (skin and subcutaneous fat) approaches near maximal values at skin temperatures of 30° C., with the onset of vasoconstriction occurring at skin temperatures of 32-33° C. Thus, the heat loss advantage obtained by widening the core-to-skin temperature gradient with constant cooling is progressively reduced by increased superficial shell insulation as skin temperature drops below 32° C.
A primary object of the present invention is to reduce the amount of power required for body cooling and/or heating. This and other objects of the invention are achieved by using skin temperature feedback to control the cooling or heating of the body. In one embodiment, the skin temperature is maintained between a high temperature of about 35 degrees Centigrade and a low temperature of about 33 degrees Centigrade.
Further objects, features and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings.